Dietary surveys indicate that large sub-groups of the United States population are subclinically deficient in ascorbic acid (AA). Studies in animal models from our laboratory and others suggest that subclinical AA deficiency impairs the conversion of cholesterol to bile acid, a metabolic defect that may predispose to cholesterol accumulation and atherosclerosis as well as cholesterol cholelithiasis. To better define the relationship between subclinical AA deficinecy and sterol metabolism we plan the following experiments: A. Measurement of bile acid kinetics (by iostope dilution) and gallbladder bile lipid composition in a group of normal human subjects at two points in time: after 2 weeks on an AA deficient diet supplemented with 45 mg/day of AA, and again after 6-8 weeks on the same diet without AA supplementation. B. Determination of the long-term effects of AA deficiency and excess by measurement of bile acid isotope dilution parameters in guinea pigs on diets deficient in AA, diets supplemented with physiologic amounts of AA, and diets supplemented with massive amounts of AA. Measurements will be performed afte 7, 14, and 21 weeks on these diets and will be supplemented with measurements of activity of both 7 alpha-hydroxylase and hydroxymethylglutaryl-CoA-reductase, the rate limiting enzymes in bile acid and cholesterol biosynthesis respectively. C. Determination of maximal rates of bile acid production in AA deficient and control guinea pigs by measurement of bile acid output from a complete bile fistula. Sensitivity of synthesis to negative feedback inhibition will subsequently be tested in these same animals by intravenously infusing graded doses of bile acid (labelled with (C14) to correct measured output of bile acid for infused bile acid). D. Determination of bile acid sulfates and isotope dilution parameters of bile acid metabolism in guinea pigs fed ascorbic acid-2-sulfate, a derivative which lowers plasma cholesterol, perhaps through enhancement of sterol sulfation.